During the last decade my laboratory has focused on two primary questions relating to the process of meiosis in Drosophila melanogaster females; namely, how do chromosomes identify their partners; and what events ensure segregation at anaphase 1? As a consequence of that work, some aspects of meiotic segregation can now be understood in terms of specific proteins acting at defined sites on the chromosomes or on the meiotic spindle. The major lesson from this work is that the chromosomes themselves play the dominant role in both organizing the spindle and controlling the movement of the oocyte through meiosis. To extend these studies, we propose to identify new genes essential for meiosis by P element screens for meiotic mutations. We will execute two separate P-element mobilization screens; both of which are designed to isolate a large number of mutations in genes required for pairing, exchange, and/or segregation. Taken together, these screens are designed to examine equal to or more than 2O,OOO new insertions of the placW enhancer trap element. From this collection of mutation we propose to identify those genes that play crucial roles either in the events of early meiotic pairing or the processes that allow normal spindle assembly and chromosome segregation. New mutations will initially be identified by a simple genetic assay for nondisjunction or by a sterility associated with the production of normal numbers of structurally normal eggs. These mutations will then be characterized by confocal microscopy to identify mutations with strong recombination-defects or with obvious defects on spindle assembly or meiotic chromosome movement. We propose to determine the wildtype functions of these genes by characterizing the phenotypes of loss function mutations. Finally, we propose to identify the protein products of these genes by molecular analysis.